562 



UNGULATES. 



rhinocerotic type, and lacking the marked curvature of the crown characterising 

 those of the toxodonts. The vertebras of the neck are comparatively short, with 

 flattened articular surfaces, and the lateral canal piercing the transverse process in 

 the ordinary manner*. The wrist and ankle-joints were probably of the linear 

 type; the calcaneum articulated largely with the fibula; and the astragalus was 

 quite flat, and furnished with a large head for articulation with the navicular bone. 

 The femur, when known, had a large third trochanter. 



In both families the upper cheek-teeth were of a rhinocerotic type of structure, 

 having a continuous external wall undivided into lobes. The group is widely 

 distinguished from the Amblypoda by the structure of the cheek-teeth, and not 

 improbably by the number of digits having been three in place of five. It is, 

 however, decidedly the most generalised of the three South American extinct 

 suborders, as is especially shown by the flattened astragalus. The remarkable 



similarity of the molars of 

 Astrajwtherium to those of 

 rhinoceroses must probably 

 be considered as largely due 

 to parallelism, since the 

 structure of the ankle in 

 the allied Homalodonto- 

 iheviwm, indicates that the 

 group diverged from the 

 common ancestor before the 

 modern Odd-toed Ungulates 

 had acquired their charac- 

 teristic foot-structure. 



In the homalodonto- 

 there, representing the first 

 family, the teeth, as shown 

 in the accompanying figure, 

 comprise the full number of 



*H> c i> V%> m h an d have 

 no gap ; the canines being 

 rooted and of relatively 

 small size, and the molars 

 with comparatively short 

 crowns. The upper pre- 

 molars are nearly as complex as the molars; and the third upper molar is not 

 very markedly different from the two preceding teeth. The lower molars are 

 in the form of double crescents, of which the anterior develops a loop like 

 that found in the horses. It is stated that the toes terminated in claws. The 

 one known species of the genus was an animal of the approximate size of the 

 Sumatran rhinoceros. 



The gigantic astrapothere, which alone represents the second family, differs 

 from the last genus by the more specialised and reduced dentition, the enlarged 

 teeth of each jaw taking the form of permanently growing tusks, which are worn 



PALATE OF THE HOMALODONTOTHERE, WANTING SOME OF THE 

 front teeth (much reduced). 



